In the field of computer networking, a “stacking system” or “stack” is a group of physical network devices that are linked together to operate as a single, logical network device. Each member device of a stack is known as a unit and includes stacking ports for connecting with other units in the same stack, and as well as data ports for connecting with upstream/downstream hosts and/or networks.
In some stack implementations, the stacking ports of a unit can be configured to operate in one of two different communication modes: a data mode and a stacking mode. Such stacking ports are referred to as flexible stacking ports. This capability allows the flexible stacking ports to utilize a high-performance stacking protocol when set to stacking mode. This capability also allows the flexible stacking ports to be used as regular data ports when set to data mode, which can be useful in scenarios where the unit is deployed as a standalone unit (i.e., not as part of a stack). Generally speaking, a user/administrator of the unit can configure a desired communication mode for a given flexible stacking port via one or more command line interface (CLI) commands. The unit can then apply this user-configured communication mode to set the actual communication mode that is employed by the port firmware/hardware at runtime.
One complication with implementing flexible stacking ports (and other similar ports that support multiple communication modes) is that two units in a stack may unable to communicate with each other upon being connected via their respective flexible stacking ports if there is a mismatch in communication modes. For example, consider a stack that comprises a unit A with a flexible stacking port P1. Assume that an administrator initially configures P1 to operate in stacking mode. Further assume that the administrator later connects a new unit B to unit A by linking P1 of A to a flexible stacking port P2 of B, where P2 is configured to operate in data mode. In this scenario, since the communication mode of P1 (i.e., stacking mode) does not match the communication mode of P2 (i.e., data mode), units A and B may be unable to exchange data over the link connecting P1 and P2 due to, e.g., protocol or signaling incompatibilities between the two modes.
It is possible to avoid this problem by having the administrator manually set the configuration of P2 (using the CLI command(s) mentioned above) to operate in stacking mode prior to connecting ports P2 and P1 together. However, such manual configuration can be cumbersome to perform in large-scale stacking deployments and can prevent the use of automated stack creation processes. Further, in cases where a link between two flexible stacking ports that was previously working goes down (due to, e.g., an inadvertent mode change of one port), it may not be clear to the administrator which port needs to be reconfigured or which communication mode should be used.